By Harvey Black
As concern and controversy swirl about the Zika virus, Argentinian researchers have developed a new trap that can be used to effectively monitor and control the Aedes aegypti mosquito, which is the primary transmitter of Zika, dengue, chikungunya, and yellow fever. The trap is described in the Journal of Medical Entomology.
The plastic ovitrap is a small, handle-less cup made of low-density polyethylene (LDPE) that has been infused with the larvicide pyriproxyfen. When the cup is filled with water, the larvicide is immediately released from the plastic.
Female Aedes aegypti mosquitoes prefer to deposit eggs in small containers such as pots and tires that contain water, so the trap is an attractive egg-laying location.
“This is a great idea,” said Grayson Brown, an entomologist at the University of Kentucky, who was not involved in the research. “Pyriproxyfen likes to move around in the environment. Molding it into the plastic like that keeps it where you put it.”
Dr. Brown thinks that the cups would be most effective on a neighborhood basis, with perhaps one or two cups in the equivalent of a back yard. He also believes that the concept of pyriproxyfen embedded in plastic can go well-beyond the small cups used in the study.
“When I read through the paper, I immediately started thinking of disposable liners for drain pans and outside potted plants, and disposable liners for bird baths,” he said.
Pyriproxyfen has gained notoriety through false reports by activists who claimed that it caused microcephaly. However, that claim was debunked by the Entomological Society of America, and by scientists such as Ian Musgrave of the University of Adelaide, who stated, “In a variety of animal species, even enormous quantities of pyriproxyfen do not cause the defects seen during the recent Zika outbreak. Pyriproxyfen is poorly absorbed by humans and rapidly broken down so even the minute amounts humans would be exposed to via water treatment would be reduced even further.”
The Brazilian government also stated that the association between the use of pyriproxyfen and microcephaly has no scientific basis.
Pyriproxyfen is a juvenile hormone analog that prevents insect larvae from developing into adults. It is one of several pesticides recommended by the World Health Organization Pesticide Evaluation Scheme.
Although ovitraps have been used for decades as a means of conducting mosquito surveillance, the use of plastic containing the larvicide pyriproxyfen is a new development in the effort to control mosquitoes. In their study, the researchers tested the trap on laboratory-raised Aedes aegypti mosquitoes and reported that the larvicide was 100 percent effective in preventing the larvae from developing into adults.
One problem with this delivery system, noted Brown, is that the pyriproxyfen-containing cups are subject to the vagaries of weather and human activity. Rain can wash the cups away, or people can knock them over.
Laura Harburguer, lead researcher of the team that developed the traps, acknowledges that people can upset the traps, and she plans to prevent that by involving people in the communities where the traps are used. Another concern is that pyriproxyfen can be partially inactivated by sunlight, so the cups may work best when placed in the shade, which may be advantageous since Aedes aegypti mosquitoes prefer being in the shade, according to Dr. Brown.
As enthusiastic as he is about this new trap, Brown cautions it is hardly a “silver bullet.”
“This is another potential tool [to control mosquitoes], and we need all the tools we can get,” he said.
Dr. Harburguer said that the scientists are preparing to do field trials of the trap in the fall, and that they are testing attractants to preferentially lure the mosquitoes to the ovitraps.
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Harvey Black is a freelance science writer. A long-time resident of Madison, Wisconsin, he has written for numerous publications including Environmental Health Perspectives, Scientific American Mind, New Scientist, The Scientist, and the Milwaukee Journal Sentinel.